This is the original green wall - not a 20-foot-high panel expertly planted with tropicals in the atrium of a corporate HQ, like Dansko, which is profiled in the paper's Home & Design section today. This one dates to the 1920s. It's the rock wall garden at Morris Arboretum. Six feet high, planted with alpines, it's in the rose garden, which is just about to burst open. The wall is already blooming. When I visited, there was a little fog, an empty bench. Perfect atmospherics.
If you'd like to read more about Dansko's wall, and other kinds of green walls, go to http://www.philly.com/inquirer/living/